Stanford identifies its preferred approach for the future of Searsville Dam and Reservoir
After extensive study of Searsville Dam and Reservoir, a Stanford committee recommends that the university develop and evaluate, in collaboration with resource agencies, two alternative ways to achieve fish passage, while avoiding an increase in downstream or upstream flooding and also preserving and providing riparian and wetlands habitats.
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Stanford University has completed an extensive, four-year study of the future of Searsville Dam and Reservoir and narrowed its options to two alternative approaches, both of which will improve fish passage, manage accumulated and future sediment and avoid an increase in upstream or downstream flood threats in the San Francisquito Creek watershed.
The first option would create an opening at the base of the 123-year-old Searsville Dam. The opening would allow the creek to flow through the dam and provide fish passage to upstream creeks and a level of storm water retention for downstream areas. This option is dependent on whether the accumulated fine sediment trapped behind the dam can be safely moved downstream to San Francisco Bay – a function that needs further study.
As a result of that uncertainty, Stanford will also consider a second option that would allow the reservoir to fill completely with sediment, stabilize the accumulated sediment behind the dam, facilitate development of wetlands and a new stream channel through the accumulated sediment, and include construction of a fish ladder or a rerouted passageway to provide fish passage upstream.
The next step in determining the future of Searsville Dam is for the university to continue and extend discussions with organizations that must conduct environmental reviews and authorize and permit any future changes. Those agencies include the U.S. Army Corps of Engineers, the National Marine Fisheries Service, the U.S. Fish and Wildlife Service, the California Department of Fish and Wildlife, the State Water Resources Board, the California Division of Safety of Dams, San Mateo County and the San Francisquito Joint Powers Authority. The permitting process is anticipated to take many years because of the complexity of the reviews that each agency is likely to require. Because these alternatives may involve expenditures of up to $100 million, finding ways to address funding will be a top priority.
The key issue in addressing the dam and reservoir’s future continues to be the management and disposition of approximately 2.7 million cubic yards of sediment that has built up behind the dam since its construction in 1892.
“We are confident the options we will pursue do three important things, but in different ways: enhance fish passage, minimize impacts of sediment management and provide a level of downstream storm-water protection,” said Chris Field, co-chair of the Searsville Steering Committee. Field is a professor of Earth system science and of biology, faculty director of Jasper Ridge Biological Preserve and director of the Carnegie Institution’s Department of Global Ecology.
The two options are among recommendations made by a 12-person faculty and staff committee that studied eight alternatives, each with variations, for the future of Searsville Dam and Reservoir. The committee, including scholars who specialize in engineering, environmental science, history and law, made its recommendations to President John Hennessy and Provost John Etchemendy. The committee was chaired by Field and Jean McCown, Stanford director of community relations.
If it is feasible and acceptable to allow accumulated fine sediment to move downstream to San Francisco Bay, committee members prefer the option that would create an opening in the bottom of the dam. This would allow the creek to flow through the bottom of the dam. The dam would continue to act as a “check dam” to detain and delay high creek flows from reaching the downstream stretches of the creek.
Searsville Dam, which is located in the university’s Jasper Ridge Biological Preserve, was built between 1888 and 1892 by the Spring Valley Water Co. to provide water to San Francisco. Stanford bought the dam in 1919. The university’s current study was prompted primarily by continuing sedimentation, which has reduced the reservoir to 10 percent of its original capacity.
Committee members weighed such issues as research and educational activities at Jasper Ridge, university water supply needs, the environmental effects of the dam on both upstream and downstream habitats and wetlands, the needs of endangered species and storm-water risks. They considered alternatives ranging from removing the dam to doing nothing and allowing the sediment to fill in the reservoir.
“The key question is whether – and how – the sediment can be moved downstream,” McCown said. “The Steering Committee concluded that mechanical dredging, drying and hauling the sediment to disposal sites would create considerable environmental disturbances for our neighbors and at Jasper Ridge. We estimate that removing the sediment through dredging would take nine or 10 years and encompass some 150,000 truck trips.”
McCown added, “The possibility of releasing the sediment downstream, which has been done in other projects, presents a unique challenge that we must continue studying to ensure that we do the right thing, especially for the communities located downstream of the dam.
“Our preferred approach does not preclude the possibility of someday removing the dam. But we have to be confident we don’t need the check-dam function and that removal wouldn’t cause unacceptable negative biological impacts in the watershed.”
The sediment, the result of the highly friable nature of rocks in the Santa Cruz Mountains, has been the key concern for committee members since their study began in 2011. The sediment is both fine and coarse. The fine sediment would likely flow to San Francisco Bay, nourishing salt marsh habitat. However, the disposition of the coarse sediment, which stabilizes the marsh area upstream of the dam, must be managed differently to minimize the potential to reduce channel capacity.
Another concern has been the welfare of Central California Coast steelhead in the watershed. Steelhead, which are threatened, hatch and spend the early part of their lives in freshwater creeks in the San Francisquito Creek watershed. They live most of their lives at sea and return to their freshwater creek of origin to spawn. Committee members believe enhanced fish passage can be achieved through either option because both would connect San Francisquito Creek to a new riparian channel leading upstream to Corte Madera Creek.
Searsville Dam and Reservoir
The Searsville Dam is located within the San Francisquito Creek watershed, which encompasses about 50 square miles and more than 20 creeks. Many of the streams merge halfway between the mountains and the bay into San Francisquito Creek, which marks the boundary between Santa Clara and San Mateo counties. Over thousands of years, the creek has carried sediment downstream from the Santa Cruz Mountains to create the alluvial fan upon which Atherton, Menlo Park, Palo Alto, East Palo Alto and Stanford were developed.
The reservoir created by the dam was once a popular recreational area. The Stanford Board of Trustees formally designated Jasper Ridge as a biological preserve in 1973 and, in 1975, ended recreational use of Searsville Reservoir. Since that time, Searsville Dam and Reservoir have played a key role in the Jasper Ridge Biological Preserve’s research and education mission. More than 70 research projects are currently being conducted at the preserve, which has been the site of leading climate studies.
Water from the Searsville Reservoir is used for irrigation, agricultural and fire protection purposes. Those diversions have been suspended since early 2013 because of the current drought. The committee recommends that the Searsville water diversion be relocated downstream with expanded storage at Felt Lake Reservoir as a replacement water storage facility. Stanford’s diversions at San Francisquito Creek are limited to higher-flow conditions that provide sufficient flows for fish passage, even while diversions are occurring.
Stanford obtains its drinking water from the Hetch Hetchy Reservoir in the Sierra Nevada. Non-potable water comes from groundwater and local surface water, including Felt Lake.
Searsville Dam is a concrete gravity structure that has been certified as structurally sound by the state of California. It is 68 feet high, 275 feet wide and made of interlocking concrete blocks. Five creeks – Westridge, Dennis Martin, Corte Madera, Sausal and Alambique – empty into Searsville Reservoir. About 85 percent of the inflow for the reservoir comes from the Corte Madera Creek.